299 doc restructure

Here's my first stab at this.

The idea is to trim the main README down to "everything you need to know in 5 minutes", and then break out the rest into topic documents.
If an error occurs while using the API within Drupal, a custom exception is thrown. All the exceptions thrown by the RESTful module extend the ``\RestfulException``.

```php
try {
  // Use the Drupal API version.
}
catch (\RestfulException $e) {
  watchdog_exception($e);
}